Explain Why a Phenotype Might Not Always Indicate a Genotype

Fulmer, 2009 BIO

GENETIC CROSSES

Differentiate: Genotype

Phenotype

Homozygous

Heterozygous

Explain why a phenotype might not always indicate a genotype.

Probability:

Probability = Number of times an event is EXPECTED to happen Number of times an event COULD happen

Mendel’s experiments: Dominant trait occurred 6,022 Recessive trait occurred 2,001 What is the probability that the dominant trait will occur? Expressed as a percentage: Expressed as a ratio:

What is the probability that the recessive trait will occur? Expressed as a percentage: Expressed as a ratio: Fulmer, 2009 BIO

PREDICTING RESULT OF MONOHYBRID CROSSES

Monohybrid cross is . . .

HOMOZYGOUS X HOMOZYGOUS

Trait: Flower Color Dominant- PP purple Recessive- pp white Phenotype: Genotype:

HOMOZYGOUS X HETEROZYGOUS

Trait: Coat Color Dominant- BB black Recessive- bb brown Phenotype: Genotype:

HETEROZYGOUS X HETEROZYGOUS

Trait: Plant Height Dominant- TT tall Recessive- tt short Phenotype: Genotype: Fulmer, 2009 BIO

TESTCROSS

Can determine the genotype of any individual whose phenotype expresses the dominant trait, but is unknown if individual is actually homozygous or heterozygous for a trait.

Trait: Pod shape Dominant: II -Inflated Recessive: ii -Constricted Phenotype: Genotype:

INCOMPLETE DOMINANCE

-Occurs when the phenotype of a heterozygote is intermediate between the phenotypes determined by the dominant and recessive traits.

Trait: Flower Color Dominant: RR -Red Recessive: rr -White Phenotype: Genotype:

CODOMINANCE

-Occurs when both alleles for a gene are expressed in a heterozygous offspring. Trait: Blood Types Fulmer, 2009 BIO

DIHYBRID CROSSES

-Cross in which two characteristics are tracked. Thus four alleles from each parent can combine.

HOMOZYGOUS X HOMOZYGOUS

Trait: Seed texture Dominant: RR – Round Recessive: rr- Wrinkled

Seed color Dominant: YY – Yellow Recessive: yy – Green Phenotype: Genotype: Fulmer, 2009 BIO

HETEROZYGOUS X HETEROZYGOUS

Trait: Seed texture Dominant: RR – Round Recessive: rr- Wrinkled

Seed color Dominant: YY – Yellow Recessive: yy – Green Phenotype: Genotype: